Using photogrammetry to assess the recovery of a cypress forest and its impact on water-borne erosion. Case study: Guadalupe Island.

Abstract

Abstract We used photogrammetry to assess and monitor the recovery of the cypress forest on Guadalupe Island, Mexico, an ecosystem impaired by fires and overgrazing. Two drone surveys were conducted over the forest area during the summers of 2016 and 2019 with natural color (RGB) and near infrared (NIR) cameras. It is the first complete 3D reconstruction of the cypress forest on the island. The image process products were the canopy height model (CHM), digital surface model (DSM), and digital terrain model (DTM), which were used to calculate the number, density, and height of the trees. The CHM highly correlates with the forest's structure, R = 0.92, according to field measurements of the trees' heights and geo-position. Results account for ~ 67,340 trees higher than two meters in 2019 and a horizontal expansion of 134 ha from 2016 to 2019. Over 90% of the cypress population were young trees between 2 and 3 m that recovered after an extensive fire in 2008. We developed a novel method to calculate the C cover factor of the Revised Universal Soil Loss Equation (RUSLE) using CHM and DSM obtained by photogrammetry. Modeled erosion rates vary from 0 to 2 Kg m− 2 y− 1 in areas with trees of different ages to values ​greater than 15 Kg m− 2 y− 1 in areas with steep slopes. According to our results, the derived products from photogrammetry point clouds allow us to describe the vertical structure of the cypress forest with high accuracy and resolution and calculate the cover factor of RUSLE.